Recently, in response to social needs or movement with the background of energy and environmental issues, a fuel cell has been noticed as a vehicle drive source and a stationary power source. A fuel cell is classified into various types based on electrolyte types or electrode types, including, as typical ones, an alkali type, a phosphoric acid type, a molten carbonate salt type, a solid electrolyte type and a proton-exchange membrane type. Among these, because of operability at low temperature (usually equal to or lower than 100° C.), a proton-exchange membrane fuel cell (PEFC) has been noticed, and development and practical applications thereof have recently been progressing as a low pollution type power source for an automobile. Although as applications of PEFC, a vehicle drive source or a stationary power source has been studied, durability over a long period is required for these applications.
In an electrode catalyst layer, where a cell reaction proceeds in a fuel cell, a catalyst, a carrier supporting the catalyst and a proton conductive polyelectrolyte (an ionomer) have been usually included, and an electrode catalyst layer of a three-dimensional void structure has been formed by binding a carrier or a carrier supporting a catalyst using an ionomer as a binder. In this case, a noble metal such as platinum or the like, or an alloy containing a noble metal element has been known as a catalyst, and a conductive carbon material represented by carbon black has been known as a carrier. As a method for supporting a platinum catalyst onto a carbon material, a method which comprises using a strongly acidic raw material such as platinum chloride, platinum nitrate to support an active species onto the surface of a carbon material, dinitrodiamine platinate or the like, and drying the supported material at equal to or lower than 200° C., has been adopted (for example, see JP-A-2004-139789, in particular, paragraphs from (0041) to (0043)).
In PEFC, however, the inside of an anode catalyst layer is generally purged with air to remove fuel (hydrogen) included therein, when operation is stopped, and supply of fuel (hydrogen) in re-start operation forms a local cell in the anode catalyst layer, which makes the inside of a cathode catalyst layer exposed in high voltage (equal to or higher than about 0.8 V). Then, exposure to high voltage would induce hydrolysis of a noble metal such as platinum or the like to generate oxygen, which results in oxidative corrosion of a carbon material at the vicinity of the noble metal, and destruction of the electrode layer structure (the three-dimensional void structure). Further, such destruction of three-dimensional void structure by progress of oxidative corrosion of a carbon material caused by repeated start-stop operations would reduce gas diffusivity or drainage of generated water, increase concentration over-voltage amount, induce flooding easily, and deteriorate power generation performance. In addition, it would incur a problem of elution of a noble metal as catalyst such as platinum or the like, and result in accelerated decomposition of an ionomer.